As an available technique for measuring radiation distribution, there is a radiation detection apparatus which includes a radiation detection system having a scintillating optical fiber converting an incident radiation to a light signal; light receiving elements respectively connected to both ends of the scintillating optical fiber and converting the light signals propagating in two directions along the scintillating optical fiber into electric signals; and a radiation analysis system deriving the incident position of the radiation on the basis of the difference between the arrival times of the electric signals from the two light receiving elements. Methods for obtaining two- or three-dimensional radiation distribution using this technique are disclosed, for example, in Japanese Patent Laid-open Specification No. 9-15335/1997 and the like.
For the purpose of measuring the positional distribution of a radiation in a satisfactory accuracy, a large number of detectors such as scintillating optical fibers small in diameter are bundled, and a photon-counting device including a large number of photomultipliers or position sensitive photomultipliers are connected to the rear ends of the detectors. In this constitution of the measurement apparatus, the photons emitted from the scintillators are counted, and thus, the measurement is conducted as to which scintillator the radiation has reached.
However, in the case where a radiation is incident from afar, the radiation comes to be a case of parallel incidence, so that it is impossible to determine the incident position and direction by merely using scintillating optical fibers. In this connection, there is considered an apparatus in which a large number of directional radiation detectors oriented in various directions are simultaneously arranged, but such an apparatus probably comes to be large in size and heavy in weight, and thus impractical.